Paint spray booths are enclosures in which industrial production painting operations are performed. They are used by the automotive industry and by other manufacturers to spray automotive bodies and other products. Paint spray booths provide a clean environment for paint application, and separate the solvents from the solids in the paint.
In the process of spraying such articles, overspray tends to coat the interior surfaces of the booth with multiple layers of paint. Depending on the type of paint, this overspray could be tacky or relatively dry. In fact, in commercial paint spraying operations, frequently as much as 50% of the paint used is not deposited on the object to be painted.
The present practice is to remove accumulated overspray paint from the interior walls and surfaces of these booths through the use of solvent based strippers, either alone or coupled with scrubbing, or through the use of high pressured water blasting. In water blasting, a stream of water of up to 12,000 psi is sprayed at the paint, by a machine similar to the one disclosed in U.S. Pat. No. 4,218,155 issued to Goerss. The high pressure facilitates the removal of the paint. Under either the stripper or water blasting method, the paint is then deposited into water wash systems used to scrub the overspray particles from the exhaust air. For example, in the relatively newer type of paint spray booths, known as down draft booths, the air from the paint spray booths passes through steel grates in the floor into the wash water below, where the paint particles are detackified.
As a consequence of use, the interior surfaces of the paint spray booth including the steel grates, become covered with paint. This paint buildup can restrict the air flow from the booth, which in turn can cause air flow imbalances within the booth. Additionally, as the paint build ups, it creates a fire hazard due to its low flash point. Further, the buildup creates an occupational safety hazard as the floor becomes slippery and sticky.
Typically paint spray booths are cleaned daily. Under existing technology, it is not uncommon to find 6-10 men assigned to clean a 200 foot long permanently installed booth. Additionally, some facilities utilize small modular booths. Especially in the modular type of facility, due to space limitations, cleaning the grates is often accompanied by their being manually removed from the booth and manually cleaned elsewhere, although some permanently installed booths have their grates cleaned the same way. Since not all of these grates are the same size, a problem can arise at the time the grates are to be reinstalled in that one or more grates may be returned to an incorrect booth. Since some manufacturing facilities incorporate up to 20 or more booths, it can be appreciated that a large investment in man-hours and money is involved in the cleaning of paint spray booths.
An additional problem has been created in that many of the current paint products incorporate oligomers instead of the polymers commonly found in older paints, such that attempted removal of these paints is made more difficult, since they have a tendency towards tacky elasticity. For example, newer solvent borne paints will not cure at room temperature. These paints will remain sticky or tacky for long periods of time. Additional problems are created in that if the paint removed is flushed into the water wash, globs of non-detackified paint can clog the scrubber sections and transfer lines of the paint booth, sometimes resulting in the need to manually clean the system, which translates into downtime and additional labor costs for the entire system.
At one time a number of paint spray booths cleaners included methylene chloride strippers. However, this type of product suffers serious drawbacks in that the chemical methylene chloride is extremely undesirable, in that it is a possible carcinogen.
In the past, inert water-based-material or vinyl coatings have been used to precoat paint spray booths. An example of this is U.S. Pat. No. 4,548,967 issued to Brown, et al for a water soluble paint spray booth precoat comprising water, sugar, a plasticizer and polyvinyl pyrollidone. Another similar compound is disclosed in U.S. Pat. No. 4,748,049 issued to Charles, et al for a paint booth coating comprising an aqueous solution of polyvinyl alcohol, a foam depressor and a wetting agent. The above two organic paint spray booth coatings permit the paint overspray to be physically taken off by peeling or by a manual scraper. However, the polyvinyl pyrollidone and polyvinyl alcohol are extremely water sensitive, such that the performance of either of the above coatings is impaired at high relative humidity.
A further drawback of all of the aforementioned systems is that they are only capable of removing the paint associated with the upper portion of the grates, and as discussed above, the leftover paint can constitute a hazard. Additionally, the Brown et al and Charles et al coatings do not include specific teachings of their use on grates. A further problem encountered by the use of high pressure spraying is that if the wash water is too close to the grate, a back spray can be produced, thereby re-introducing tacky paint and undesirable chemicals back into the paint spray booth and back into the presence of the individuals assigned the task of cleaning the booth.
Recently a new organic based barrier coating has been developed which features the use of an organic blowing agent. The only known method for utilization of this coating has been via dipping, and it must be remembered that the formulation for a dippable barrier coating may not necessarily work in spray application form. This organic barrier coating releases a large amount of nitrogen when its temperature is raised to 195.degree. F.
The use of a blowing agent in a barrier coating represents a radical departure from the prior art, since blowing agents are conventionally used in plastic molding operations. Their typical decomposition temperatures, at which temperatures they generate gases, are greater than 250.degree. F., a temperature too high for use in paint spray booths given the low flash points of some solvents. Furthermore, the components of an organic based barrier coating with an organic blowing agent are relatively expensive and many water based organic coatings encounter drying time problems in booths with relatively high humidity.
With the exception of the single dippable organic based barrier coating discussed above, the approach of industry has been to improve the barrier coatings already in use and/or to utilize improved solvents as paint strippers. This is especially true with respect to sprayable barrier coatings. Unfortunately, the use of strippers poses an environmental, as well as a health-related, potential for danger.
It is thus apparent that the need exists for an improved barrier coating which provides for the safe and effective removal of paint overspray.